push: teach --force-with-lease to smart-http transport

[git.git] / transport-helper.c

#include "cache.h"
#include "transport.h"
#include "quote.h"
#include "run-command.h"
#include "commit.h"
#include "diff.h"
#include "revision.h"
#include "quote.h"
#include "remote.h"
#include "string-list.h"
#include "thread-utils.h"
#include "sigchain.h"
#include "argv-array.h"
#include "refs.h"

static int debug;

struct helper_data {
        const char *name;
        struct child_process *helper;
        FILE *out;
        unsigned fetch : 1,
                import : 1,
                bidi_import : 1,
                export : 1,
                option : 1,
                push : 1,
                connect : 1,
                signed_tags : 1,
                no_disconnect_req : 1;
        char *export_marks;
        char *import_marks;
        /* These go from remote name (as in "list") to private name */
        struct refspec *refspecs;
        int refspec_nr;
        /* Transport options for fetch-pack/send-pack (should one of
         * those be invoked).
         */
        struct git_transport_options transport_options;
};

static void sendline(struct helper_data *helper, struct strbuf *buffer)
{
        if (debug)
                fprintf(stderr, "Debug: Remote helper: -> %s", buffer->buf);
        if (write_in_full(helper->helper->in, buffer->buf, buffer->len)
                != buffer->len)
                die_errno("Full write to remote helper failed");
}

static int recvline_fh(FILE *helper, struct strbuf *buffer, const char *name)
{
        strbuf_reset(buffer);
        if (debug)
                fprintf(stderr, "Debug: Remote helper: Waiting...\n");
        if (strbuf_getline(buffer, helper, '\n') == EOF) {
                if (debug)
                        fprintf(stderr, "Debug: Remote helper quit.\n");
                exit(128);
        }

        if (debug)
                fprintf(stderr, "Debug: Remote helper: <- %s\n", buffer->buf);
        return 0;
}

static int recvline(struct helper_data *helper, struct strbuf *buffer)
{
        return recvline_fh(helper->out, buffer, helper->name);
}

static void xchgline(struct helper_data *helper, struct strbuf *buffer)
{
        sendline(helper, buffer);
        recvline(helper, buffer);
}

static void write_constant(int fd, const char *str)
{
        if (debug)
                fprintf(stderr, "Debug: Remote helper: -> %s", str);
        if (write_in_full(fd, str, strlen(str)) != strlen(str))
                die_errno("Full write to remote helper failed");
}

static const char *remove_ext_force(const char *url)
{
        if (url) {
                const char *colon = strchr(url, ':');
                if (colon && colon[1] == ':')
                        return colon + 2;
        }
        return url;
}

static void do_take_over(struct transport *transport)
{
        struct helper_data *data;
        data = (struct helper_data *)transport->data;
        transport_take_over(transport, data->helper);
        fclose(data->out);
        free(data);
}

static struct child_process *get_helper(struct transport *transport)
{
        struct helper_data *data = transport->data;
        struct argv_array argv = ARGV_ARRAY_INIT;
        struct strbuf buf = STRBUF_INIT;
        struct child_process *helper;
        const char **refspecs = NULL;
        int refspec_nr = 0;
        int refspec_alloc = 0;
        int duped;
        int code;
        char git_dir_buf[sizeof(GIT_DIR_ENVIRONMENT) + PATH_MAX + 1];
        const char *helper_env[] = {
                git_dir_buf,
                NULL
        };


        if (data->helper)
                return data->helper;

        helper = xcalloc(1, sizeof(*helper));
        helper->in = -1;
        helper->out = -1;
        helper->err = 0;
        argv_array_pushf(&argv, "git-remote-%s", data->name);
        argv_array_push(&argv, transport->remote->name);
        argv_array_push(&argv, remove_ext_force(transport->url));
        helper->argv = argv_array_detach(&argv, NULL);
        helper->git_cmd = 0;
        helper->silent_exec_failure = 1;

        snprintf(git_dir_buf, sizeof(git_dir_buf), "%s=%s", GIT_DIR_ENVIRONMENT, get_git_dir());
        helper->env = helper_env;

        code = start_command(helper);
        if (code < 0 && errno == ENOENT)
                die("Unable to find remote helper for '%s'", data->name);
        else if (code != 0)
                exit(code);

        data->helper = helper;
        data->no_disconnect_req = 0;

        /*
         * Open the output as FILE* so strbuf_getline() can be used.
         * Do this with duped fd because fclose() will close the fd,
         * and stuff like taking over will require the fd to remain.
         */
        duped = dup(helper->out);
        if (duped < 0)
                die_errno("Can't dup helper output fd");
        data->out = xfdopen(duped, "r");

        write_constant(helper->in, "capabilities\n");

        while (1) {
                const char *capname;
                int mandatory = 0;
                recvline(data, &buf);

                if (!*buf.buf)
                        break;

                if (*buf.buf == '*') {
                        capname = buf.buf + 1;
                        mandatory = 1;
                } else
                        capname = buf.buf;

                if (debug)
                        fprintf(stderr, "Debug: Got cap %s\n", capname);
                if (!strcmp(capname, "fetch"))
                        data->fetch = 1;
                else if (!strcmp(capname, "option"))
                        data->option = 1;
                else if (!strcmp(capname, "push"))
                        data->push = 1;
                else if (!strcmp(capname, "import"))
                        data->import = 1;
                else if (!strcmp(capname, "bidi-import"))
                        data->bidi_import = 1;
                else if (!strcmp(capname, "export"))
                        data->export = 1;
                else if (!data->refspecs && !prefixcmp(capname, "refspec ")) {
                        ALLOC_GROW(refspecs,
                                   refspec_nr + 1,
                                   refspec_alloc);
                        refspecs[refspec_nr++] = xstrdup(capname + strlen("refspec "));
                } else if (!strcmp(capname, "connect")) {
                        data->connect = 1;
                } else if (!strcmp(capname, "signed-tags")) {
                        data->signed_tags = 1;
                } else if (!prefixcmp(capname, "export-marks ")) {
                        struct strbuf arg = STRBUF_INIT;
                        strbuf_addstr(&arg, "--export-marks=");
                        strbuf_addstr(&arg, capname + strlen("export-marks "));
                        data->export_marks = strbuf_detach(&arg, NULL);
                } else if (!prefixcmp(capname, "import-marks")) {
                        struct strbuf arg = STRBUF_INIT;
                        strbuf_addstr(&arg, "--import-marks=");
                        strbuf_addstr(&arg, capname + strlen("import-marks "));
                        data->import_marks = strbuf_detach(&arg, NULL);
                } else if (mandatory) {
                        die("Unknown mandatory capability %s. This remote "
                            "helper probably needs newer version of Git.",
                            capname);
                }
        }
        if (refspecs) {
                int i;
                data->refspec_nr = refspec_nr;
                data->refspecs = parse_fetch_refspec(refspec_nr, refspecs);
                for (i = 0; i < refspec_nr; i++)
                        free((char *)refspecs[i]);
                free(refspecs);
        } else if (data->import || data->bidi_import || data->export) {
                warning("This remote helper should implement refspec capability.");
        }
        strbuf_release(&buf);
        if (debug)
                fprintf(stderr, "Debug: Capabilities complete.\n");
        return data->helper;
}

static int disconnect_helper(struct transport *transport)
{
        struct helper_data *data = transport->data;
        int res = 0;

        if (data->helper) {
                if (debug)
                        fprintf(stderr, "Debug: Disconnecting.\n");
                if (!data->no_disconnect_req) {
                        /*
                         * Ignore write errors; there's nothing we can do,
                         * since we're about to close the pipe anyway. And the
                         * most likely error is EPIPE due to the helper dying
                         * to report an error itself.
                         */
                        sigchain_push(SIGPIPE, SIG_IGN);
                        xwrite(data->helper->in, "\n", 1);
                        sigchain_pop(SIGPIPE);
                }
                close(data->helper->in);
                close(data->helper->out);
                fclose(data->out);
                res = finish_command(data->helper);
                argv_array_free_detached(data->helper->argv);
                free(data->helper);
                data->helper = NULL;
        }
        return res;
}

static const char *unsupported_options[] = {
        TRANS_OPT_UPLOADPACK,
        TRANS_OPT_RECEIVEPACK,
        TRANS_OPT_THIN,
        TRANS_OPT_KEEP
        };
static const char *boolean_options[] = {
        TRANS_OPT_THIN,
        TRANS_OPT_KEEP,
        TRANS_OPT_FOLLOWTAGS
        };

static int set_helper_option(struct transport *transport,
                          const char *name, const char *value)
{
        struct helper_data *data = transport->data;
        struct strbuf buf = STRBUF_INIT;
        int i, ret, is_bool = 0;

        get_helper(transport);

        if (!data->option)
                return 1;

        for (i = 0; i < ARRAY_SIZE(unsupported_options); i++) {
                if (!strcmp(name, unsupported_options[i]))
                        return 1;
        }

        for (i = 0; i < ARRAY_SIZE(boolean_options); i++) {
                if (!strcmp(name, boolean_options[i])) {
                        is_bool = 1;
                        break;
                }
        }

        strbuf_addf(&buf, "option %s ", name);
        if (is_bool)
                strbuf_addstr(&buf, value ? "true" : "false");
        else
                quote_c_style(value, &buf, NULL, 0);
        strbuf_addch(&buf, '\n');

        xchgline(data, &buf);

        if (!strcmp(buf.buf, "ok"))
                ret = 0;
        else if (!prefixcmp(buf.buf, "error")) {
                ret = -1;
        } else if (!strcmp(buf.buf, "unsupported"))
                ret = 1;
        else {
                warning("%s unexpectedly said: '%s'", data->name, buf.buf);
                ret = 1;
        }
        strbuf_release(&buf);
        return ret;
}

static void standard_options(struct transport *t)
{
        char buf[16];
        int n;
        int v = t->verbose;

        set_helper_option(t, "progress", t->progress ? "true" : "false");

        n = snprintf(buf, sizeof(buf), "%d", v + 1);
        if (n >= sizeof(buf))
                die("impossibly large verbosity value");
        set_helper_option(t, "verbosity", buf);
}

static int release_helper(struct transport *transport)
{
        int res = 0;
        struct helper_data *data = transport->data;
        free_refspec(data->refspec_nr, data->refspecs);
        data->refspecs = NULL;
        res = disconnect_helper(transport);
        free(transport->data);
        return res;
}

static int fetch_with_fetch(struct transport *transport,
                            int nr_heads, struct ref **to_fetch)
{
        struct helper_data *data = transport->data;
        int i;
        struct strbuf buf = STRBUF_INIT;

        standard_options(transport);

        for (i = 0; i < nr_heads; i++) {
                const struct ref *posn = to_fetch[i];
                if (posn->status & REF_STATUS_UPTODATE)
                        continue;

                strbuf_addf(&buf, "fetch %s %s\n",
                            sha1_to_hex(posn->old_sha1), posn->name);
        }

        strbuf_addch(&buf, '\n');
        sendline(data, &buf);

        while (1) {
                recvline(data, &buf);

                if (!prefixcmp(buf.buf, "lock ")) {
                        const char *name = buf.buf + 5;
                        if (transport->pack_lockfile)
                                warning("%s also locked %s", data->name, name);
                        else
                                transport->pack_lockfile = xstrdup(name);
                }
                else if (!buf.len)
                        break;
                else
                        warning("%s unexpectedly said: '%s'", data->name, buf.buf);
        }
        strbuf_release(&buf);
        return 0;
}

static int get_importer(struct transport *transport, struct child_process *fastimport)
{
        struct child_process *helper = get_helper(transport);
        struct helper_data *data = transport->data;
        struct argv_array argv = ARGV_ARRAY_INIT;
        int cat_blob_fd, code;
        memset(fastimport, 0, sizeof(*fastimport));
        fastimport->in = helper->out;
        argv_array_push(&argv, "fast-import");
        argv_array_push(&argv, debug ? "--stats" : "--quiet");

        if (data->bidi_import) {
                cat_blob_fd = xdup(helper->in);
                argv_array_pushf(&argv, "--cat-blob-fd=%d", cat_blob_fd);
        }
        fastimport->argv = argv.argv;
        fastimport->git_cmd = 1;

        code = start_command(fastimport);
        return code;
}

static int get_exporter(struct transport *transport,
                        struct child_process *fastexport,
                        struct string_list *revlist_args)
{
        struct helper_data *data = transport->data;
        struct child_process *helper = get_helper(transport);
        int argc = 0, i;
        memset(fastexport, 0, sizeof(*fastexport));

        /* we need to duplicate helper->in because we want to use it after
         * fastexport is done with it. */
        fastexport->out = dup(helper->in);
        fastexport->argv = xcalloc(6 + revlist_args->nr, sizeof(*fastexport->argv));
        fastexport->argv[argc++] = "fast-export";
        fastexport->argv[argc++] = "--use-done-feature";
        fastexport->argv[argc++] = data->signed_tags ?
                "--signed-tags=verbatim" : "--signed-tags=warn-strip";
        if (data->export_marks)
                fastexport->argv[argc++] = data->export_marks;
        if (data->import_marks)
                fastexport->argv[argc++] = data->import_marks;

        for (i = 0; i < revlist_args->nr; i++)
                fastexport->argv[argc++] = revlist_args->items[i].string;

        fastexport->git_cmd = 1;
        return start_command(fastexport);
}

static int fetch_with_import(struct transport *transport,
                             int nr_heads, struct ref **to_fetch)
{
        struct child_process fastimport;
        struct helper_data *data = transport->data;
        int i;
        struct ref *posn;
        struct strbuf buf = STRBUF_INIT;

        get_helper(transport);

        if (get_importer(transport, &fastimport))
                die("Couldn't run fast-import");

        for (i = 0; i < nr_heads; i++) {
                posn = to_fetch[i];
                if (posn->status & REF_STATUS_UPTODATE)
                        continue;

                strbuf_addf(&buf, "import %s\n", posn->name);
                sendline(data, &buf);
                strbuf_reset(&buf);
        }

        write_constant(data->helper->in, "\n");
        /*
         * remote-helpers that advertise the bidi-import capability are required to
         * buffer the complete batch of import commands until this newline before
         * sending data to fast-import.
         * These helpers read back data from fast-import on their stdin, which could
         * be mixed with import commands, otherwise.
         */

        if (finish_command(&fastimport))
                die("Error while running fast-import");
        argv_array_free_detached(fastimport.argv);

        /*
         * The fast-import stream of a remote helper that advertises
         * the "refspec" capability writes to the refs named after the
         * right hand side of the first refspec matching each ref we
         * were fetching.
         *
         * (If no "refspec" capability was specified, for historical
         * reasons we default to the equivalent of *:*.)
         *
         * Store the result in to_fetch[i].old_sha1.  Callers such
         * as "git fetch" can use the value to write feedback to the
         * terminal, populate FETCH_HEAD, and determine what new value
         * should be written to peer_ref if the update is a
         * fast-forward or this is a forced update.
         */
        for (i = 0; i < nr_heads; i++) {
                char *private;
                posn = to_fetch[i];
                if (posn->status & REF_STATUS_UPTODATE)
                        continue;
                if (data->refspecs)
                        private = apply_refspecs(data->refspecs, data->refspec_nr, posn->name);
                else
                        private = xstrdup(posn->name);
                if (private) {
                        read_ref(private, posn->old_sha1);
                        free(private);
                }
        }
        strbuf_release(&buf);
        return 0;
}

static int process_connect_service(struct transport *transport,
                                   const char *name, const char *exec)
{
        struct helper_data *data = transport->data;
        struct strbuf cmdbuf = STRBUF_INIT;
        struct child_process *helper;
        int r, duped, ret = 0;
        FILE *input;

        helper = get_helper(transport);

        /*
         * Yes, dup the pipe another time, as we need unbuffered version
         * of input pipe as FILE*. fclose() closes the underlying fd and
         * stream buffering only can be changed before first I/O operation
         * on it.
         */
        duped = dup(helper->out);
        if (duped < 0)
                die_errno("Can't dup helper output fd");
        input = xfdopen(duped, "r");
        setvbuf(input, NULL, _IONBF, 0);

        /*
         * Handle --upload-pack and friends. This is fire and forget...
         * just warn if it fails.
         */
        if (strcmp(name, exec)) {
                r = set_helper_option(transport, "servpath", exec);
                if (r > 0)
                        warning("Setting remote service path not supported by protocol.");
                else if (r < 0)
                        warning("Invalid remote service path.");
        }

        if (data->connect)
                strbuf_addf(&cmdbuf, "connect %s\n", name);
        else
                goto exit;

        sendline(data, &cmdbuf);
        recvline_fh(input, &cmdbuf, name);
        if (!strcmp(cmdbuf.buf, "")) {
                data->no_disconnect_req = 1;
                if (debug)
                        fprintf(stderr, "Debug: Smart transport connection "
                                "ready.\n");
                ret = 1;
        } else if (!strcmp(cmdbuf.buf, "fallback")) {
                if (debug)
                        fprintf(stderr, "Debug: Falling back to dumb "
                                "transport.\n");
        } else
                die("Unknown response to connect: %s",
                        cmdbuf.buf);

exit:
        fclose(input);
        return ret;
}

static int process_connect(struct transport *transport,
                                     int for_push)
{
        struct helper_data *data = transport->data;
        const char *name;
        const char *exec;

        name = for_push ? "git-receive-pack" : "git-upload-pack";
        if (for_push)
                exec = data->transport_options.receivepack;
        else
                exec = data->transport_options.uploadpack;

        return process_connect_service(transport, name, exec);
}

static int connect_helper(struct transport *transport, const char *name,
                   const char *exec, int fd[2])
{
        struct helper_data *data = transport->data;

        /* Get_helper so connect is inited. */
        get_helper(transport);
        if (!data->connect)
                die("Operation not supported by protocol.");

        if (!process_connect_service(transport, name, exec))
                die("Can't connect to subservice %s.", name);

        fd[0] = data->helper->out;
        fd[1] = data->helper->in;
        return 0;
}

static int fetch(struct transport *transport,
                 int nr_heads, struct ref **to_fetch)
{
        struct helper_data *data = transport->data;
        int i, count;

        if (process_connect(transport, 0)) {
                do_take_over(transport);
                return transport->fetch(transport, nr_heads, to_fetch);
        }

        count = 0;
        for (i = 0; i < nr_heads; i++)
                if (!(to_fetch[i]->status & REF_STATUS_UPTODATE))
                        count++;

        if (!count)
                return 0;

        if (data->fetch)
                return fetch_with_fetch(transport, nr_heads, to_fetch);

        if (data->import)
                return fetch_with_import(transport, nr_heads, to_fetch);

        return -1;
}

static int push_update_ref_status(struct strbuf *buf,
                                   struct ref **ref,
                                   struct ref *remote_refs)
{
        char *refname, *msg;
        int status;

        if (!prefixcmp(buf->buf, "ok ")) {
                status = REF_STATUS_OK;
                refname = buf->buf + 3;
        } else if (!prefixcmp(buf->buf, "error ")) {
                status = REF_STATUS_REMOTE_REJECT;
                refname = buf->buf + 6;
        } else
                die("expected ok/error, helper said '%s'", buf->buf);

        msg = strchr(refname, ' ');
        if (msg) {
                struct strbuf msg_buf = STRBUF_INIT;
                const char *end;

                *msg++ = '\0';
                if (!unquote_c_style(&msg_buf, msg, &end))
                        msg = strbuf_detach(&msg_buf, NULL);
                else
                        msg = xstrdup(msg);
                strbuf_release(&msg_buf);

                if (!strcmp(msg, "no match")) {
                        status = REF_STATUS_NONE;
                        free(msg);
                        msg = NULL;
                }
                else if (!strcmp(msg, "up to date")) {
                        status = REF_STATUS_UPTODATE;
                        free(msg);
                        msg = NULL;
                }
                else if (!strcmp(msg, "non-fast forward")) {
                        status = REF_STATUS_REJECT_NONFASTFORWARD;
                        free(msg);
                        msg = NULL;
                }
                else if (!strcmp(msg, "already exists")) {
                        status = REF_STATUS_REJECT_ALREADY_EXISTS;
                        free(msg);
                        msg = NULL;
                }
                else if (!strcmp(msg, "fetch first")) {
                        status = REF_STATUS_REJECT_FETCH_FIRST;
                        free(msg);
                        msg = NULL;
                }
                else if (!strcmp(msg, "needs force")) {
                        status = REF_STATUS_REJECT_NEEDS_FORCE;
                        free(msg);
                        msg = NULL;
                }
                else if (!strcmp(msg, "stale info")) {
                        status = REF_STATUS_REJECT_STALE;
                        free(msg);
                        msg = NULL;
                }
        }

        if (*ref)
                *ref = find_ref_by_name(*ref, refname);
        if (!*ref)
                *ref = find_ref_by_name(remote_refs, refname);
        if (!*ref) {
                warning("helper reported unexpected status of %s", refname);
                return 1;
        }

        if ((*ref)->status != REF_STATUS_NONE) {
                /*
                 * Earlier, the ref was marked not to be pushed, so ignore the ref
                 * status reported by the remote helper if the latter is 'no match'.
                 */
                if (status == REF_STATUS_NONE)
                        return 1;
        }

        (*ref)->status = status;
        (*ref)->remote_status = msg;
        return !(status == REF_STATUS_OK);
}

static void push_update_refs_status(struct helper_data *data,
                                    struct ref *remote_refs)
{
        struct strbuf buf = STRBUF_INIT;
        struct ref *ref = remote_refs;
        for (;;) {
                char *private;

                recvline(data, &buf);
                if (!buf.len)
                        break;

                if (push_update_ref_status(&buf, &ref, remote_refs))
                        continue;

                if (!data->refspecs)
                        continue;

                /* propagate back the update to the remote namespace */
                private = apply_refspecs(data->refspecs, data->refspec_nr, ref->name);
                if (!private)
                        continue;
                update_ref("update by helper", private, ref->new_sha1, NULL, 0, 0);
                free(private);
        }
        strbuf_release(&buf);
}

static int push_refs_with_push(struct transport *transport,
                               struct ref *remote_refs, int flags)
{
        int force_all = flags & TRANSPORT_PUSH_FORCE;
        int mirror = flags & TRANSPORT_PUSH_MIRROR;
        struct helper_data *data = transport->data;
        struct strbuf buf = STRBUF_INIT;
        struct ref *ref;
        struct string_list cas_options = STRING_LIST_INIT_DUP;
        struct string_list_item *cas_option;

        get_helper(transport);
        if (!data->push)
                return 1;

        for (ref = remote_refs; ref; ref = ref->next) {
                if (!ref->peer_ref && !mirror)
                        continue;

                /* Check for statuses set by set_ref_status_for_push() */
                switch (ref->status) {
                case REF_STATUS_REJECT_NONFASTFORWARD:
                case REF_STATUS_REJECT_STALE:
                case REF_STATUS_REJECT_ALREADY_EXISTS:
                case REF_STATUS_UPTODATE:
                        continue;
                default:
                        ; /* do nothing */
                }

                if (force_all)
                        ref->force = 1;

                strbuf_addstr(&buf, "push ");
                if (!ref->deletion) {
                        if (ref->force)
                                strbuf_addch(&buf, '+');
                        if (ref->peer_ref)
                                strbuf_addstr(&buf, ref->peer_ref->name);
                        else
                                strbuf_addstr(&buf, sha1_to_hex(ref->new_sha1));
                }
                strbuf_addch(&buf, ':');
                strbuf_addstr(&buf, ref->name);
                strbuf_addch(&buf, '\n');

                /*
                 * The "--force-with-lease" options without explicit
                 * values to expect have already been expanded into
                 * the ref->old_sha1_expect[] field; we can ignore
                 * transport->smart_options->cas altogether and instead
                 * can enumerate them from the refs.
                 */
                if (ref->expect_old_sha1) {
                        struct strbuf cas = STRBUF_INIT;
                        strbuf_addf(&cas, "%s:%s",
                                    ref->name, sha1_to_hex(ref->old_sha1_expect));
                        string_list_append(&cas_options, strbuf_detach(&cas, NULL));
                }
        }
        if (buf.len == 0) {
                string_list_clear(&cas_options, 0);
                return 0;
        }

        standard_options(transport);
        for_each_string_list_item(cas_option, &cas_options)
                set_helper_option(transport, "cas", cas_option->string);

        if (flags & TRANSPORT_PUSH_DRY_RUN) {
                if (set_helper_option(transport, "dry-run", "true") != 0)
                        die("helper %s does not support dry-run", data->name);
        }

        strbuf_addch(&buf, '\n');
        sendline(data, &buf);
        strbuf_release(&buf);

        push_update_refs_status(data, remote_refs);
        return 0;
}

static int push_refs_with_export(struct transport *transport,
                struct ref *remote_refs, int flags)
{
        struct ref *ref;
        struct child_process *helper, exporter;
        struct helper_data *data = transport->data;
        struct string_list revlist_args = STRING_LIST_INIT_NODUP;
        struct strbuf buf = STRBUF_INIT;

        if (!data->refspecs)
                die("remote-helper doesn't support push; refspec needed");

        if (flags & TRANSPORT_PUSH_DRY_RUN) {
                if (set_helper_option(transport, "dry-run", "true") != 0)
                        die("helper %s does not support dry-run", data->name);
        }

        helper = get_helper(transport);

        write_constant(helper->in, "export\n");

        strbuf_reset(&buf);

        for (ref = remote_refs; ref; ref = ref->next) {
                char *private;
                unsigned char sha1[20];

                if (ref->deletion)
                        die("remote-helpers do not support ref deletion");

                private = apply_refspecs(data->refspecs, data->refspec_nr, ref->name);
                if (private && !get_sha1(private, sha1)) {
                        strbuf_addf(&buf, "^%s", private);
                        string_list_append(&revlist_args, strbuf_detach(&buf, NULL));
                        hashcpy(ref->old_sha1, sha1);
                }
                free(private);

                if (ref->deletion)
                        die("remote-helpers do not support ref deletion");

                if (ref->peer_ref) {
                        if (strcmp(ref->peer_ref->name, ref->name))
                                die("remote-helpers do not support old:new syntax");
                        string_list_append(&revlist_args, ref->peer_ref->name);
                }
        }

        if (get_exporter(transport, &exporter, &revlist_args))
                die("Couldn't run fast-export");

        if (finish_command(&exporter))
                die("Error while running fast-export");
        push_update_refs_status(data, remote_refs);
        return 0;
}

static int push_refs(struct transport *transport,
                struct ref *remote_refs, int flags)
{
        struct helper_data *data = transport->data;

        if (process_connect(transport, 1)) {
                do_take_over(transport);
                return transport->push_refs(transport, remote_refs, flags);
        }

        if (!remote_refs) {
                fprintf(stderr, "No refs in common and none specified; doing nothing.\n"
                        "Perhaps you should specify a branch such as 'master'.\n");
                return 0;
        }

        if (data->push)
                return push_refs_with_push(transport, remote_refs, flags);

        if (data->export)
                return push_refs_with_export(transport, remote_refs, flags);

        return -1;
}


static int has_attribute(const char *attrs, const char *attr) {
        int len;
        if (!attrs)
                return 0;

        len = strlen(attr);
        for (;;) {
                const char *space = strchrnul(attrs, ' ');
                if (len == space - attrs && !strncmp(attrs, attr, len))
                        return 1;
                if (!*space)
                        return 0;
                attrs = space + 1;
        }
}

static struct ref *get_refs_list(struct transport *transport, int for_push)
{
        struct helper_data *data = transport->data;
        struct child_process *helper;
        struct ref *ret = NULL;
        struct ref **tail = &ret;
        struct ref *posn;
        struct strbuf buf = STRBUF_INIT;

        helper = get_helper(transport);

        if (process_connect(transport, for_push)) {
                do_take_over(transport);
                return transport->get_refs_list(transport, for_push);
        }

        if (data->push && for_push)
                write_str_in_full(helper->in, "list for-push\n");
        else
                write_str_in_full(helper->in, "list\n");

        while (1) {
                char *eov, *eon;
                recvline(data, &buf);

                if (!*buf.buf)
                        break;

                eov = strchr(buf.buf, ' ');
                if (!eov)
                        die("Malformed response in ref list: %s", buf.buf);
                eon = strchr(eov + 1, ' ');
                *eov = '\0';
                if (eon)
                        *eon = '\0';
                *tail = alloc_ref(eov + 1);
                if (buf.buf[0] == '@')
                        (*tail)->symref = xstrdup(buf.buf + 1);
                else if (buf.buf[0] != '?')
                        get_sha1_hex(buf.buf, (*tail)->old_sha1);
                if (eon) {
                        if (has_attribute(eon + 1, "unchanged")) {
                                (*tail)->status |= REF_STATUS_UPTODATE;
                                read_ref((*tail)->name, (*tail)->old_sha1);
                        }
                }
                tail = &((*tail)->next);
        }
        if (debug)
                fprintf(stderr, "Debug: Read ref listing.\n");
        strbuf_release(&buf);

        for (posn = ret; posn; posn = posn->next)
                resolve_remote_symref(posn, ret);

        return ret;
}

int transport_helper_init(struct transport *transport, const char *name)
{
        struct helper_data *data = xcalloc(sizeof(*data), 1);
        data->name = name;

        if (getenv("GIT_TRANSPORT_HELPER_DEBUG"))
                debug = 1;

        transport->data = data;
        transport->set_option = set_helper_option;
        transport->get_refs_list = get_refs_list;
        transport->fetch = fetch;
        transport->push_refs = push_refs;
        transport->disconnect = release_helper;
        transport->connect = connect_helper;
        transport->smart_options = &(data->transport_options);
        return 0;
}

/*
 * Linux pipes can buffer 65536 bytes at once (and most platforms can
 * buffer less), so attempt reads and writes with up to that size.
 */
#define BUFFERSIZE 65536
/* This should be enough to hold debugging message. */
#define PBUFFERSIZE 8192

/* Print bidirectional transfer loop debug message. */
static void transfer_debug(const char *fmt, ...)
{
        va_list args;
        char msgbuf[PBUFFERSIZE];
        static int debug_enabled = -1;

        if (debug_enabled < 0)
                debug_enabled = getenv("GIT_TRANSLOOP_DEBUG") ? 1 : 0;
        if (!debug_enabled)
                return;

        va_start(args, fmt);
        vsnprintf(msgbuf, PBUFFERSIZE, fmt, args);
        va_end(args);
        fprintf(stderr, "Transfer loop debugging: %s\n", msgbuf);
}

/* Stream state: More data may be coming in this direction. */
#define SSTATE_TRANSFERING 0
/*
 * Stream state: No more data coming in this direction, flushing rest of
 * data.
 */
#define SSTATE_FLUSHING 1
/* Stream state: Transfer in this direction finished. */
#define SSTATE_FINISHED 2

#define STATE_NEEDS_READING(state) ((state) <= SSTATE_TRANSFERING)
#define STATE_NEEDS_WRITING(state) ((state) <= SSTATE_FLUSHING)
#define STATE_NEEDS_CLOSING(state) ((state) == SSTATE_FLUSHING)

/* Unidirectional transfer. */
struct unidirectional_transfer {
        /* Source */
        int src;
        /* Destination */
        int dest;
        /* Is source socket? */
        int src_is_sock;
        /* Is destination socket? */
        int dest_is_sock;
        /* Transfer state (TRANSFERRING/FLUSHING/FINISHED) */
        int state;
        /* Buffer. */
        char buf[BUFFERSIZE];
        /* Buffer used. */
        size_t bufuse;
        /* Name of source. */
        const char *src_name;
        /* Name of destination. */
        const char *dest_name;
};

/* Closes the target (for writing) if transfer has finished. */
static void udt_close_if_finished(struct unidirectional_transfer *t)
{
        if (STATE_NEEDS_CLOSING(t->state) && !t->bufuse) {
                t->state = SSTATE_FINISHED;
                if (t->dest_is_sock)
                        shutdown(t->dest, SHUT_WR);
                else
                        close(t->dest);
                transfer_debug("Closed %s.", t->dest_name);
        }
}

/*
 * Tries to read read data from source into buffer. If buffer is full,
 * no data is read. Returns 0 on success, -1 on error.
 */
static int udt_do_read(struct unidirectional_transfer *t)
{
        ssize_t bytes;

        if (t->bufuse == BUFFERSIZE)
                return 0;       /* No space for more. */

        transfer_debug("%s is readable", t->src_name);
        bytes = read(t->src, t->buf + t->bufuse, BUFFERSIZE - t->bufuse);
        if (bytes < 0 && errno != EWOULDBLOCK && errno != EAGAIN &&
                errno != EINTR) {
                error("read(%s) failed: %s", t->src_name, strerror(errno));
                return -1;
        } else if (bytes == 0) {
                transfer_debug("%s EOF (with %i bytes in buffer)",
                        t->src_name, t->bufuse);
                t->state = SSTATE_FLUSHING;
        } else if (bytes > 0) {
                t->bufuse += bytes;
                transfer_debug("Read %i bytes from %s (buffer now at %i)",
                        (int)bytes, t->src_name, (int)t->bufuse);
        }
        return 0;
}

/* Tries to write data from buffer into destination. If buffer is empty,
 * no data is written. Returns 0 on success, -1 on error.
 */
static int udt_do_write(struct unidirectional_transfer *t)
{
        ssize_t bytes;

        if (t->bufuse == 0)
                return 0;       /* Nothing to write. */

        transfer_debug("%s is writable", t->dest_name);
        bytes = write(t->dest, t->buf, t->bufuse);
        if (bytes < 0 && errno != EWOULDBLOCK && errno != EAGAIN &&
                errno != EINTR) {
                error("write(%s) failed: %s", t->dest_name, strerror(errno));
                return -1;
        } else if (bytes > 0) {
                t->bufuse -= bytes;
                if (t->bufuse)
                        memmove(t->buf, t->buf + bytes, t->bufuse);
                transfer_debug("Wrote %i bytes to %s (buffer now at %i)",
                        (int)bytes, t->dest_name, (int)t->bufuse);
        }
        return 0;
}


/* State of bidirectional transfer loop. */
struct bidirectional_transfer_state {
        /* Direction from program to git. */
        struct unidirectional_transfer ptg;
        /* Direction from git to program. */
        struct unidirectional_transfer gtp;
};

static void *udt_copy_task_routine(void *udt)
{
        struct unidirectional_transfer *t = (struct unidirectional_transfer *)udt;
        while (t->state != SSTATE_FINISHED) {
                if (STATE_NEEDS_READING(t->state))
                        if (udt_do_read(t))
                                return NULL;
                if (STATE_NEEDS_WRITING(t->state))
                        if (udt_do_write(t))
                                return NULL;
                if (STATE_NEEDS_CLOSING(t->state))
                        udt_close_if_finished(t);
        }
        return udt;     /* Just some non-NULL value. */
}

#ifndef NO_PTHREADS

/*
 * Join thread, with apporiate errors on failure. Name is name for the
 * thread (for error messages). Returns 0 on success, 1 on failure.
 */
static int tloop_join(pthread_t thread, const char *name)
{
        int err;
        void *tret;
        err = pthread_join(thread, &tret);
        if (!tret) {
                error("%s thread failed", name);
                return 1;
        }
        if (err) {
                error("%s thread failed to join: %s", name, strerror(err));
                return 1;
        }
        return 0;
}

/*
 * Spawn the transfer tasks and then wait for them. Returns 0 on success,
 * -1 on failure.
 */
static int tloop_spawnwait_tasks(struct bidirectional_transfer_state *s)
{
        pthread_t gtp_thread;
        pthread_t ptg_thread;
        int err;
        int ret = 0;
        err = pthread_create(&gtp_thread, NULL, udt_copy_task_routine,
                &s->gtp);
        if (err)
                die("Can't start thread for copying data: %s", strerror(err));
        err = pthread_create(&ptg_thread, NULL, udt_copy_task_routine,
                &s->ptg);
        if (err)
                die("Can't start thread for copying data: %s", strerror(err));

        ret |= tloop_join(gtp_thread, "Git to program copy");
        ret |= tloop_join(ptg_thread, "Program to git copy");
        return ret;
}
#else

/* Close the source and target (for writing) for transfer. */
static void udt_kill_transfer(struct unidirectional_transfer *t)
{
        t->state = SSTATE_FINISHED;
        /*
         * Socket read end left open isn't a disaster if nobody
         * attempts to read from it (mingw compat headers do not
         * have SHUT_RD)...
         *
         * We can't fully close the socket since otherwise gtp
         * task would first close the socket it sends data to
         * while closing the ptg file descriptors.
         */
        if (!t->src_is_sock)
                close(t->src);
        if (t->dest_is_sock)
                shutdown(t->dest, SHUT_WR);
        else
                close(t->dest);
}

/*
 * Join process, with apporiate errors on failure. Name is name for the
 * process (for error messages). Returns 0 on success, 1 on failure.
 */
static int tloop_join(pid_t pid, const char *name)
{
        int tret;
        if (waitpid(pid, &tret, 0) < 0) {
                error("%s process failed to wait: %s", name, strerror(errno));
                return 1;
        }
        if (!WIFEXITED(tret) || WEXITSTATUS(tret)) {
                error("%s process failed", name);
                return 1;
        }
        return 0;
}

/*
 * Spawn the transfer tasks and then wait for them. Returns 0 on success,
 * -1 on failure.
 */
static int tloop_spawnwait_tasks(struct bidirectional_transfer_state *s)
{
        pid_t pid1, pid2;
        int ret = 0;

        /* Fork thread #1: git to program. */
        pid1 = fork();
        if (pid1 < 0)
                die_errno("Can't start thread for copying data");
        else if (pid1 == 0) {
                udt_kill_transfer(&s->ptg);
                exit(udt_copy_task_routine(&s->gtp) ? 0 : 1);
        }

        /* Fork thread #2: program to git. */
        pid2 = fork();
        if (pid2 < 0)
                die_errno("Can't start thread for copying data");
        else if (pid2 == 0) {
                udt_kill_transfer(&s->gtp);
                exit(udt_copy_task_routine(&s->ptg) ? 0 : 1);
        }

        /*
         * Close both streams in parent as to not interfere with
         * end of file detection and wait for both tasks to finish.
         */
        udt_kill_transfer(&s->gtp);
        udt_kill_transfer(&s->ptg);
        ret |= tloop_join(pid1, "Git to program copy");
        ret |= tloop_join(pid2, "Program to git copy");
        return ret;
}
#endif

/*
 * Copies data from stdin to output and from input to stdout simultaneously.
 * Additionally filtering through given filter. If filter is NULL, uses
 * identity filter.
 */
int bidirectional_transfer_loop(int input, int output)
{
        struct bidirectional_transfer_state state;

        /* Fill the state fields. */
        state.ptg.src = input;
        state.ptg.dest = 1;
        state.ptg.src_is_sock = (input == output);
        state.ptg.dest_is_sock = 0;
        state.ptg.state = SSTATE_TRANSFERING;
        state.ptg.bufuse = 0;
        state.ptg.src_name = "remote input";
        state.ptg.dest_name = "stdout";

        state.gtp.src = 0;
        state.gtp.dest = output;
        state.gtp.src_is_sock = 0;
        state.gtp.dest_is_sock = (input == output);
        state.gtp.state = SSTATE_TRANSFERING;
        state.gtp.bufuse = 0;
        state.gtp.src_name = "stdin";
        state.gtp.dest_name = "remote output";

        return tloop_spawnwait_tasks(&state);
}